Control of passive soot oxidation

ABSTRACT

A system and method for controlling passive soot oxidation in a diesel particulate filter that includes sensing the temperature of exhaust gases upstream and downstream of the diesel particulate filter. The sensed temperatures are used by a control unit to predict whether the temperature of the exhaust gas within the diesel particulate is within a predetermined temperature range for passive oxidation of soot in the diesel particulate filter. If the temperatures are below passive oxidation temperatures, an auxiliary component is activated that increases the temperature of exhaust gas delivered to the diesel particulate filter. When the exhaust gas temperature within the DPF is predicted to be within passive oxidation levels but below active regeneration temperatures, the auxiliary component is deactivated.

BACKGROUND

Combustion engines may employ emission controls or systems that are configured to reduce the amount of nitrogen oxides (NOx), such as nitrogen dioxide, present in the engine's exhaust gas. One aspect of controlling such emissions may include the use of a particulate filter. For example, diesel engines may employ a diesel particulate filter (DPF) that has porous ceramics that allow gases to flow through the filter while also trapping solid particulate matter, such as, for example, soot.

Different approaches may be employed to remove soot that has accumulated in the DPF. For example, soot may be removed from the DPF through passive regeneration, which uses hot exhaust gases entering into the DPF and NO₂ present in the exhaust gas or formed catalytically to oxidize the soot. The temperatures at which passive regeneration may be initiated may vary depending on a variety of different factors, including the level of NOx or soot in the exhaust, among other factors. In some systems, a slow degree of passive regeneration in the DPF may be initiated at around 250° C., with the rate of regeneration increasing as the temperature of the exhaust gas in the DPF increases, such as, for example, when the exhaust temperature in the DPF reaches around 300° C. However, under certain engine operating conditions and/or environments, the exhaust gas entering the DPF may not reach temperatures needed for passive soot oxidation in the DPF. For example, operating the engine for relatively short time periods, when the engine is idling, or while the associated vehicle is parked, may prevent the temperature of the exhaust gas entering into the DPF from reaching temperatures necessary for passive soot oxidation. In such situations, undesirable amounts of particulate matter may accumulate in the DPF. Such accumulation of particulate matter may require that the DPF occasionally be removed from the emission system to be cleaned or replaced.

Another approach to cleaning the DPF is the use of an active regeneration event. With active regeneration, the exhaust gas is increased to temperatures exceeding those used for passive regeneration. For example, in some systems, active regeneration may occur where exhaust gas temperatures are around, or above, 550° C. According to some systems, the elevated temperature of the exhaust gas entering the DPF may be generated in the diesel oxidation catalyst (DOC). For example, additional fuel may be supplied to the DOC, such as injecting additional fuel in the cylinder or the exhaust stream upstream of the DOC. The DOC then consumes the fuel, resulting in an exothermic reaction in the DOC that may elevate the temperature of the exhaust gas that will flow downstream to the DPF to around and/or above 550° C. However, there may be a relatively high fuel penalty associated with increasing the temperature of the exhaust gas to active regeneration levels. Additionally, the occasional injection of such fuel may require significant integration with the engine's operation, such as, for example, integration with an engine control unit (ECU). Yet, such integration may not be possible for some applications, including, existing vehicles that already do not utilize such fuel dosing strategies to elevate exhaust gas temperatures for regeneration events. Additionally, the high exhaust temperatures attained for active regeneration may damage the DPF.

Further, in some vehicles, regeneration is not arranged to, or does not, occur while the vehicle is in-use on the road. For example, at least some existing vehicles may not be equipped to raise the temperature of the exhaust gas after the exhaust gas has exited the engine. Additionally, some existing vehicles may be limited to the degree to which the temperature of the exhaust gas may be elevated, such as being limited to the lightoff temperature of the DOC (temperature required to oxidize at least 90% of the additional fuel dosed into the exhaust). In such situations, the DPF may have to undergo forced regeneration while still in the vehicle, or be removed from the vehicle and regenerated offline or while the vehicle is parked.

SUMMARY

Embodiments described herein relate to a method for controlling passive soot oxidation in a diesel particulate filter. The method includes sensing a temperature of an exhaust gas delivered to the diesel particulate filter and sensing a temperature of the exhaust gas released out of the diesel particulate filter. Additionally, an electronic control module predicts a temperature of the exhaust gas within the diesel particulate filter using the sensed temperatures of the exhaust gas delivered to and released out of the diesel particulate filter. The electronic control module also determines whether the predicted exhaust gas temperature is within a predetermined temperature range for passive oxidation of soot within the diesel particulate filter. An auxiliary component is activated to increase the temperature of the exhaust gas delivered to the diesel particulate filter to a passive soot oxidation temperature when the predicted exhaust gas temperature within the diesel particulate filter is determined to be below the predetermined temperature range.

Another embodiment relates to a system for monitoring and heating exhaust gas to control passive soot oxidation. The system includes a diesel particulate filter and first and second temperature sensors positioned upstream and downstream of the diesel particulate filter, respectively. The first temperature sensor is configured to detect the temperature of the exhaust gas delivered to the diesel particulate filter, while the second temperature sensor is configured to detect the temperature of the exhaust gas flowing out of the diesel particulate filter. The system also includes an auxiliary component that is configured to elevate the temperature of exhaust gas delivered to the diesel particulate filter when the auxiliary component is activated. Additionally, a control module is configured to predict a first temperature of the exhaust gas within the diesel particulate filter based on the temperature sensed by the first and second temperature sensors before the auxiliary component is activated. The control module is also configured to predict a second temperature of the exhaust gas within the diesel particulate filter based on the temperature sensed by the first and second temperature sensors before the auxiliary component is de-activated. Further, the control module is configured to activate the auxiliary component when the first temperature is below a predetermined passive soot oxidation range and deactivate the auxiliary component when the second temperature is within the predetermined passive soot oxidation range.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a function block diagram of an engine system that includes an exhaust gas treatment system having a diesel oxidation catalyst, a diesel particulate filter, and an auxiliary component.

FIG. 2 illustrates a small burner unit as an auxiliary component for heating exhaust gas upstream of the DPF.

FIG. 3 illustrates the use of an external reformer unit as an auxiliary component used in the heating exhaust gas upstream of a diesel oxidation catalyst.

FIG. 4 illustrates an auxiliary component that includes a fuel dosing unit and reformer upstream of the DPF.

FIG. 5 is a flow chart for illustrating an exemplary method for controlling passive soot oxidation for a DPF.

DETAILED DESCRIPTION

FIG. 1 is a function block diagram of an engine system 10 that includes an exhaust gas treatment system 12 having a diesel oxidation catalyst (DOC) 14, a diesel particulate filter (DPF) 16, and an auxiliary component 18. As shown, the engine system 10 includes an internal combustion engine 20, such as for example, and a diesel or gasoline. The engine system 10 may also include an exhaust manifold 22 that couples the combustion engine 20 to the exhaust gas treatment system 12. The exhaust gas treatment system 12 may include one or more exhaust pipes 24 configured to transport engine exhaust gas along the exhaust gas treatment system 12 to, and out of, a tailpipe 26. The exhaust system 12 may include the DOC 14, the auxiliary component 18, and the DPF 16. As shown in FIG. 1, the DOC 14 is positioned upstream of the DPF 16.

According to the illustrated embodiment, the auxiliary component 18 is configured to elevate, or assist in elevating, the temperature of exhaust gas upstream of the DPF 16. For example, according to certain embodiments, the auxiliary component 18 may be a burner, and reformer unit, and/or both a fuel dosing unit and a reformer. Although FIG. 1 illustrates the auxiliary component 18 as being downstream of the DOC 14, according to other embodiments, the auxiliary component 18 may be positioned upstream of the DOC 14. For at least certain vehicles, the auxiliary component 14 may be employed in lieu of, or in addition to, the lightoff temperatures obtained by the DOC 14 that may also elevate the temperature of the exhaust gas.

According to certain embodiments, the auxiliary component 18 may be used for elevating the temperature of the exhaust gas that is to enter into the DPF 16 so that the temperature within the DPF 16 is above the balance point temperature, which is the temperature at which the rate of soot oxidation is greater than the rate at which soot may accumulate in the DPF 16. The actual balance point temperature may vary due to different considerations, including the amount of NOx or soot in the exhaust gas and the catalyst formula being used in the exhaust gas treatment system 12 to convert NOx into nitrogen gas and water. For example, for certain engine systems 10, the balance point temperature may be between 250° C. and 280° C. Moreover, according to certain embodiments, the auxiliary component 14 may be used to elevate the temperature of the exhaust gas until the temperature within the DPF 16 approaches or reaches the upper temperature limit for passive regeneration. As discussed below, these heated exhaust gases are supplied to a DPF 16 that has a high thermal mass, which allows the temperature in the DPF 16 to remain in regeneration ranges for an extended period of time after the auxiliary component 18 has been at least temporarily been deactivated.

The exhaust gas treatment system 12 may also include sensors that are used to monitor the exhaust gas treatment system 12. For example, the exhaust gas treatment system 12 may include a first temperature sensor 28 (RTD1) upstream of the DPF 16 that detects the temperature of exhaust gas upstream of, or entering into, the DPF 16. Additionally, the system 12 may also include a second temperature sensor 30 downstream, or at an outlet, of the DPF 16. In the illustrated embodiment, both the first and the second temperature sensors 28, 30 may be resistance temperature detectors (RTD1, RTD2). The system 12 may also include pressure sensors 32, 34 that detect the pressure of the exhaust gas entering and exiting the DPF. For example, in the embodiment illustrated in FIG. 1, the pressure sensors 32, 34 may be part of a pressure change sensor.

Information sensed or detected by the sensors 28, 30, 32, 34 may be sent to an ECU 36, or other control unit or module, that is used to monitor the conditions of the exhaust gas entering and leaving the DPF 16. Information provided to the ECU 36, such as the pressure difference between the exhaust gas entering and exiting the DPF 16 may be used by the ECU 36 in predicting when the soot load in the DPF 16 will reach, or has reached, a level that will trigger the need for a passive regeneration event such as when the filter has greater than 3 g/l of soot. Further, the sensed temperatures of the exhaust gas entering and exiting the DPF 16 may also be used by the ECU 36 to predict whether soot is undergoing passive oxidation in the DPF 16, or whether soot may be accumulating in the DPF 16 and/or to predict the level of soot accumulation in the DPF 16. Such information may also be used to operate the auxiliary device 18 such that the exhaust gas upstream of the DPF 16 is heated to temperatures (such as above 250° C.) that may facilitate the passive oxidation of at least a portion of the accumulated soot in the DPF 16.

FIG. 2 illustrates a small burner unit 40 as an auxiliary component 18 for heating exhaust gas upstream of the DPF 16. The burner unit 40 is configured to ignite fuel to generate heat that is used to elevate the temperature of exhaust gas flowing upstream of the DPF 16 along a pipe 24. Moreover, the burner unit 40 may be configured to elevate the temperature of the exhaust gas to temperatures needed for passive regeneration in the DPF 16. For example, according to certain embodiments, the burner unit 40 may elevate the temperature of the exhaust gas to around 300° C. to as high as 400° C.

The burner unit 40 may be positioned upstream of the first temperature sensor (RTD1) 28 so that the ECU 36 may receive a signal from the temperature sensor (RTD1) 28 that is indicative of the actual temperature of the heated exhaust gas entering into the DPF 16. The second temperature sensor (RTD2) 30 is positioned to detect the temperature of the exhaust gas leaving, or downstream of, the DPF 16. Also, according to certain embodiments, pressure sensors 32, 34 are used to detect a change or difference in pressure across the DPF 16. Again, differences in the pressure of the exhaust gas entering and exiting the DPF 16 may be used to predict the level of soot accumulation in the DPF 16.

The DPF 16 maybe a high thermal mass DPF 16 that has a large thermal inertia so that the DPF 16 is able to retain heat from the elevated temperatures of the exhaust gases within the DPF 16. For example, according to certain embodiments, the DPF 16 may include materials that have high heat capacities, such as SiC and aluminum titantate. Further, the housing of the DPF 16, such as for example, the outer wall structure, may be configured to facilitate the retention of heat within the DPF 16. For example, according to certain embodiments, the DPF 16 may have an outer wall structure that has a wall thickness of around, or above, 12 mil. The ability of the DPF 16 to retain elevated temperatures may assist in extending the duration of time that the temperature within the DPF 16 is at levels necessary for passive regeneration and/or minimize the frequency at which the auxiliary component 18 needs to be activated to elevate the exhaust gas to passive regeneration temperatures. Accordingly, the exhaust gas supplied to the DPF 16 may be heated by the auxiliary component 18 to temperatures that allow the temperature inside the DPF 16 to reach the upper limit of regeneration temperatures.

FIG. 3 illustrates the use of an external reformer unit 42 as an auxiliary component 18 for heating exhaust gas upstream of the DOC 14. The external reformer unit 42 shown in FIG. 3 may convert fuel into carbon monoxide and hydrogen. Accordingly, the resulting carbon monoxide and hydrogen may flow from the external reformer unit 42 and into a supply pipe 24 so that the carbon monoxide and hydrogen mix with the exhaust gas in the pipe 24 before the exhaust gas reaches the DOC 14. The hydrogen and oxygen in the exhaust gas may then react with a catalyst in the DOC 14 to provide an exothermic reaction that elevates the temperature of the exhaust gas in, and that will be exiting, the DOC 14. For example, according to certain embodiments, the exothermic reaction may elevate the temperature of the exhaust gas exiting the DOC 14 to around 300° C. to as high as 400° C.

FIG. 4 illustrates an auxiliary component 18 that includes a fuel dosing unit 44 and a reformer 46. According to such an embodiment, fuel may be injected into the exhaust gas in the supply pipe 24 by the fuel dosing unit 44. The dosing of fuel by the fuel dosing unit 44 may be controlled by the ECU 36. The exhaust gas/fuel mixture may then be delivered by the pipe 24 to the reformer 46, which, again, may convert the fuel to hydrogen and carbon monoxide so that the exhaust gas becomes relatively rich in hydrogen content. The presence of the additional hydrogen and the temperature of the exhaust gas may result in the occurrence of an exothermic reaction that elevates the temperature of the exhaust gas. This exothermic reaction may occur in the reformer, in the pipe 24 b between the reformer 46 and the DPF 16, and/or the DPF 16.

FIG. 5 is a flow chart illustrating an exemplary method 100 for controlling passive soot oxidation for a DPF 16. At step 102, the temperature of the exhaust gas upstream or entering the DPF 16 is sensed by the first temperature sensor 28, such as, for example, a resistance temperature detector. According to certain embodiments, at step 102, the temperature of exhaust gas exiting or downstream of the DPF 16 is sensed by a second temperature sensor 30, such as, for example, by a resistance temperature detector. At step 104, a control module, such as the ECU 36 for example, may determine or predict the temperature of the exhaust gas in the DPF 16. For example, according to certain embodiments, the ECU 36 may average the temperatures sensed by the temperature sensors 28, 30 upstream and downstream of the DPF 16 to determine the temperature of the exhaust gas inside the DPF 16. However, according to other embodiments, the ECU 36 may proportion, or give different weighted value to, the temperatures sensed by the sensors 28, 30 in predicting the temperature of the exhaust gas in the DPF 16. At step 106, the control module, such as the ECU 36 again for example, may determine whether the temperature of the exhaust gas inside or entering the DPF 16 is below the desired range for passive soot oxidation. For example, although passive soot oxidation in some systems may be initiated at 250° C., according to certain embodiments, the desired range for passive soot oxidation may be around 280° C. to 320° C. The temperature ranges may be a function of catalyst formulation, Platinum Group Metal (PGM) loading, Pt/Pd ratio, exhaust O₂ levels, NO_(x)/soot levels and exhaust flow, among other possible factors. If the exhaust gas is determined at step 106 to be of sufficient temperature to oxidize the soot, or to oxidize the soot faster than the soot can accumulate within the DPF 16, the control module may continue monitoring the temperature of the exhaust gas upstream or downstream of the DPF 16 to ensure soot oxidation temperatures continue being attained in the DPF 16. Such monitoring may be continuous or occur at predetermined intervals, such as, for example, once every 5 to 30 minutes, among other predetermined intervals.

If, however, the temperature of the exhaust gas within the DPF 16 is determined at step 106 to be below soot oxidation temperatures, then at step 108 the auxiliary component 18 may be activated. Operation of the auxiliary component 18 may be controlled by the control unit. For example, the ECU 36 may issue an instruction that causes the auxiliary component 18 to be activated, such as, for example, the burner unit 40 being activated so that the burner unit 40 ignites fuel to provide heat that is used to increase the temperature of the exhaust gases upstream of the DPF 16. The heated exhaust gases may then be delivered to the DPF 16 at or above passive soot oxidation temperatures.

At step 110, the control unit, such as the ECU 36, monitors the temperature of the exhaust gas in the DPF 16. The control unit may again determine the temperature of the exhaust gas in the DPF 16 using the temperatures sensed by the temperature sensors 28, 30 upstream and downstream of the DPF 16.

Using the temperatures provided by the temperature sensors 28, 30, at step 112, the control unit determines whether the temperature of the heated exhaust gas in the DPF 16 is elevated to a desired temperature range or limit for passive regeneration in the DPF 16. For example, as previously discussed, the DPF 16 may have a high thermal mass. Accordingly, the exhaust gas heated by the auxiliary component 18 may be supplied to the DPF 16 at temperatures that are sufficient to elevate the temperature within the DPF 16 to levels that are within the range for passive soot oxidation while remaining below active soot oxidation temperatures. By heating the high thermal mass DPF 16 to temperatures at the upper range of passive regeneration temperatures, the heat retained by the DPF 16 may provide sufficient heat for passive soot oxidation to continue for an extended time period after the auxiliary component 18 has, at least for the time, been deactivated. For example, according to certain embodiments, the auxiliary component 18 may be activated for a sufficient duration and/or at sufficient temperatures so that the temperature of the heated exhaust gases supplied to the DPF 16 elevates the temperature within the DPF 16 to approximately 400° C. When the auxiliary component 18 is deactivated, heat retained by the DPF 16 may continue to be elevated before dropping to a desired regeneration temperature range, such as for, example, 280° C. to 320° C. The DPF 16 may then remain in the desired regeneration temperature for a period of time before the need to reactivated the auxiliary component 18. Thus, by initially heating a high thermal mass DPF 16 to temperatures at the upper range or limits for passive regeneration, the DPF 16 may remain at passive regeneration temperatures for an extended period of time.

If the control unit determines that the exhaust gas temperatures in the DPF 16 are at or within a predetermined passive regeneration temperature range or limit, then at step 114, the control unit may deactivate the auxiliary component 18. For example, as previously discussed, the auxiliary component 18 be operated until the temperature within the DPF 16 is at or approaching the upper temperature range or limits for passive soot oxidation while still below active regeneration temperatures. By maintaining the temperature of the exhaust gas within the DPF 16 below active regeneration temperatures, the present system may prevent or reduce the occurrence of damage to, or failure of, the DPF 16 related to exposure to the excessive temperatures associated with active regeneration, such as, for example, temperatures at or exceeding 550° C. Instead, the DPF 16 may be exposed to the lower temperatures associated with passive regeneration.

After operation of the auxiliary component 36 has been terminated, then at step 116 the control unit monitors the temperature of the exhaust gas downstream of the DPF 16. For example, the control unit may continue to monitor the exhaust gas temperature sensed by the temperature sensor 30 downstream of the DPF 16. Such monitoring may continue even when the retained heat in the high thermal mass DPF 16 is expected to allow the temperature within the DPF 16 to remain at passive soot oxidation levels. At step 118, the control unit determines whether the exhaust gas temperature downstream of the DPF 16 has decreased to a predetermined level, such as below the lower temperature limit range for passive soot oxidation, such as, for example, below 280° C., among other possible temperatures.

According to certain embodiments, the process may also include controls that are used to monitor the level of soot accumulation in the DPF 16. For example, once the temperature of the exhaust gas decreases to the predetermined level, then at step 120 the control unit initiates a timer. At step 122, the control unit may predict the soot levels accumulated to being accumulated in the DPF 16. For example, the control unit may determine or predict the level of soot accumulation in the DPF 16 over the time period that timer has been operating, after the exhaust gas temperature downstream of the DPF 16 has decreased to the predetermined level. The soot accumulated in the DPF 16 over the time period utilized at step 122 may be based on a general soot accumulation model. Various soot accumulation models may be employed, including those that predict soot accumulation in the DPF 16 based on the duration of time that the exhaust gas entering or within the DPF is at or below a predetermined temperature, engine speed and engine load, and/or engine combustion models.

Based on the level of soot accumulated in the DPF 16 as predicted at step 122, the control unit may determine whether to reactivate the auxiliary component 18 so as to elevate the temperature of exhaust gases entering into the DPF 16 to levels that will at least initiate passive soot oxidation. If the control unit re-activates the auxiliary component 18, then the process may return to step 108 and repeat the previously discussed subsequent steps.

An additional control that may be employed by the present system is the control unit predicting the soot level in the DPF 16 based on monitored differences in pressure between the exhaust gas entering and leaving the DPF 16, as shown at step 126 of FIG. 5. For example, a pressure sensor 32, 34 upstream and downstream of the DPF 16, as shown in FIGS. 1-4, may provide an indication of the soot level in the DPF 16. More specifically, as soot levels in the DPF 16 increase, the porous ceramic material of the DPF 16 may begin to be at least partially be filled with and/or blocked by soot that inhibits the flow of exhaust gas through the DPF 16, and thereby reducing the pressure of the exhaust gas exiting the DPF 16 and increasing the pressure differential measured by the pressure sensors 32, 34. Thus, the control unit may use changes and/or increases in pressure differentials across pressure sensors 32, 34 may provide information to step 124 indicating that the auxiliary component 18 is to be activated so as to increase the temperature of the exhaust gas entering the DPF 16. According to certain embodiments, step 126 may operate as a control or additional procedure to ensure that sufficient amounts of soot are being oxidized in the DPF 16. 

What is claimed is:
 1. A method for controlling passive soot oxidation in a diesel particulate filter comprising: sensing a temperature of an exhaust gas delivered to the diesel particulate filter; sensing a temperature of the exhaust gas released out of the diesel particulate filter; predicting, by an electronic control module, a temperature of the exhaust gas within the diesel particulate filter using the sensed temperatures of the exhaust gas delivered to and released out of the diesel particulate filter; determining, by the electronic control module, whether the predicted exhaust gas temperature is within a predetermined temperature range for passive soot oxidation within the diesel particulate filter; and activating an auxiliary component to increase the temperature of the exhaust gas delivered to the diesel particulate filter to a passive soot oxidation temperature when the predicted exhaust gas temperature within the diesel particulate filter is determined to be below the predetermined temperature range.
 2. The method of claim 1, further including the step of predicting, by the electronic control module, a second temperature of the exhaust gas within the diesel particulate filter while the auxiliary component is activated, and deactivating the auxiliary component when the second temperature of the exhaust gas reaches a predetermined limit, the predetermined limit being below active regeneration temperatures.
 3. The method of claim 2, wherein the method further includes monitoring the temperature of the exhaust gas downstream of the diesel particulate filter after the auxiliary component has been deactivated.
 4. The method of claim 3, further including initiating a timer after the auxiliary component has been deactivated.
 5. The method of claim 4, further including predicting the level of soot accumulation in the diesel particulate filter using a soot accumulation model.
 6. The method of claim 4, further including detecting the difference in pressure between the exhaust gas delivered to, and removed from within, the diesel particulate filter, and predicting a soot level within the diesel particulate filter using the detected pressure difference.
 7. The method of claim 1, wherein the predetermined temperature range is around 280° C. to around 320° C.
 8. A system for monitoring and heating exhaust gas to control passive soot oxidation comprising: a diesel particulate filter; a first temperature sensor positioned upstream of the diesel particulate filter, the first temperature sensor configured to detect the temperature of the exhaust gas delivered to the diesel particulate filter; a second temperature sensor positioned downstream of the diesel particulate filter, the second temperature sensor configured to detect the temperature of the exhaust gas flowing out of the diesel particulate filter; an auxiliary component configured to elevate the temperature of exhaust gas delivered to the diesel particulate filter when the auxiliary component is activated; a control module configured to predict a first temperature of the exhaust gas within the diesel particulate filter based on the temperature sensed by the first and second temperature sensors before the auxiliary component is activated and predict a second temperature of the exhaust gas within the diesel particulate filter based on the temperature sensed by the first and second temperature sensors before an activated auxiliary component is de-activated, the control module also being configured to activate the auxiliary component when the first temperature is below a predetermined passive soot oxidation temperature range, and deactivate the auxiliary component when the second temperature is within the predetermined passive soot oxidation temperature range.
 9. The system of claim 8, wherein the auxiliary component is a burner unit.
 10. The system of claim 8, wherein the auxiliary component is an external reformer unit.
 11. The system of claim 8, wherein the auxiliary component is a fuel dosing unit and a reformer.
 12. The system of claim 8, further including a first pressure sensor upstream of the diesel particulate filter and a second pressure sensor downstream of the diesel particulate filter, the control module being configured to predict a soot level in the diesel particulate filter using the difference in pressures between the first and second pressure sensors.
 13. The system of claim 8, wherein the diesel particulate filter has a large thermal inertia.
 14. The system of claim 8, wherein the first temperature is below the balance point temperature.
 15. The system of claim 8, wherein the first and second temperature sensors are resistance temperature detectors. 